I draw almost everything in flash. I prefer it over illustrator any day!!! Once you know how to use the tools, you could create a drawing like yours in a few minutes ...and you can create/save/export and import color palettes as well.

Deffo Flash. If every single frame contains...say....a 20kb image imported from illustrator, imagine the filesize of a 3000+ frame movie would be; even with compression. Not to mention the import process is an absolute pain if you're looking at an animation of that length. I even do all my still art in Flash because it's so powerful if you know how to use it. Just give it some time.